Radio direction finding apparatus



Sept. 3, 1940. c. w. EARP RADIO DIRECTION FINDING APPARATUS Filed-Oct.15, 1937 3 Sheets-Sheet 1 Sept 3, 1940- c. w. EARP RADIO DIRECTIONFINDING APPARATUS Filed Oct. l5, 1937 3 Sheets-Sheet 2 Sept. 3, 1940. Qw EARP 2,213,273'

RADIO DIRECTION FINDING APPARATUS Filed 00t- 15. 1957 3 Sheets-Sheet 3Patented Sept. 3, 1940 UNET Charles William Earp, London, England,assignor to international Standard Electric Corpora.-

tion, New York, N. Y.

Application ctober'15, 1937, Serial No. 169,198 in Great BritainFebruary 23, 1937 Claims.

rihis invention relates to methods of and apparatus for giving a directindication of the direction and/or polarisation of Waves.

An object of the invention is the provision of such a device which ismore simple in construction and more eii'icient in operation than thoseheretofore in use.

According to one feature of the invention signals received by two ormore wave collectors are modulated with different wave-forms and theresultant modulation envelopes and the original modulating Wave formsare used for operating an indicating device. The indicating device maycomprise a cathode ray oscillograph or an electro-mechanical device suchas a dynamometer.

According to a further feature of the invention three or more Wavecollectors are provided and the signals picked up from at least two ofthem are modulated before all are combined, the modulation envelope ofthe combined signals being used together with the original modulatingwave-forms for the determination 0f the direction and/or polarisation ofthe waves.

These and other features of the invention will be clear from thefollowing description taken in conjunction with the accompanyingdrawings Figs. 1 to 4. of which show four embodiments of the invention.

Reference should rst be made t0 Fig. 1 which shows schematically thearrangement according to the invention in its most general form. Anaerial system A.E.W. which gives optimum sensitivity for east-westsignals picks up a signal the strength of which is proportional to cos 0Where 0 is the bearing of the transmitting station measuredanti-clockwise from east.

This signal (e cos 0) is applied to a modulating device M.E.W. where itis modulated by a Wave form f(t) generated by the modulating generatorG.E.W. the output from the modulating device MEW. is be cos 0f(r'). Asecond aerial system A.N.S. which gives optimum sensitivity fornorth-south signals picks up a signal the strength of Which isproportional to sin 0, which is applied to a second modulating deviceM.N.S., where it is modulated by a different Wave form f' (t) by amodulating generator G.N.S. The output from the modulating device M.N.S.is ,ce sin l 0f (t). The outputs from the modulating devices M.E.W. andM.N.S. are combined in an amplifier A with the pick-up Ke from anon-directional antenna A.N.D. After detection in a detector D theoutput from D is the modulation envelope of the signal Ke produced bythe mod- E STATES PATENT @FHQE ulated outputs from the modulatingdevices The modulation envelope is applied to an indicator I, of whichtwo types are described later, to which is also applied the Wave formsfu) 5 and f(t).

envelope with fd) and f(t) in the indicator gives the. bearing of thetransmitting station as will be described later.

Fig. 2 is, in principle similar to Fig. l, but the aerial systems A.E.W.and A.N.S. are each connected to a modulator ME, MW, and lVLN, lVLS ofthe balanced type giving true north-south and east-west symmetry ofcircuit. l

Fig. 3 shows a practical embodiment-of the invention. Heptode valves VE,VW, VN andr VS, respectively in balanced relation are employed in knownmanner as combined `modulators and low frequency oscillators, the innerelec trodes of the pairs of frequency oscillators.

valves constituting low The plates of all the four valves together withthe output from a non-directional antenna A,N.D. are connected inparallel to an input of amplier A.

The resultant wave forms are indicated above the various portions of theamplier-detector circuit. In the ampliiier A, a symmetrically modulatedhigh frequency wave is shown. AAfter detection and ltering in detectorD, the low frequency wave is amplified in a low frequency amplier L F.and passed through a limiting de` vice VL which producesav square waveform, the vertical sides of which correspond to the crossing of the lowfrequency wave through Zero amplitude. The limiting device VL is of anysuitable type and in the form shown comprises a valve provided with ahigh value grid leak so that positive pulses are sharply'limited by gridcurrent and negative half cycles are limited by the bottom bend of theanode current grid vcltv age characteristic.

The peaky Wave form so produced gives an exact indication at every otherinstant at which the outputs from VE, VW, VN, VS total zero. It Will benoted that every successive instant is not indicated since half the thedevice VD.

peaks are suppressed by A comparison of the modulation v and the If,now, the wave form of one oscillator is applied to the X delector platesof a cathode ray oscillograph O, and the wave form of the otheroscillator is applied to the Y deiiector plates, eaky wave form from thedevice VD is employed to control the brilliance of the spot, forexample, by controlling the grid of the oscillograpii and causing thespot to appear only at the peaks, then a straight line from the centreoi the scale, pointing in the direction of the transmitting station,will be indicated on the oscillograph will now be demonstrated.

Referring again to Fig. 1, modulating generator G.E.W. produces awave-form f(t). This wave form is applied as i(t) to the Y deectorplates of the oscillograph causing a y or north deiiection of -f(t).Modulating generator CNS. has a wave form f(t) which is applied to the Xdeflector plates causing an x or east deection of f (t). The input tomodulator is e cos 6 from antenna A.E.W. and fd) from generator G ELW.The output of this modulator is ,uercos 0f(t), the product of thesecomponents. Similarly the output of modulator l\/I.N.S. is c sin 0]"(t).The outputs from the modulators and lVLNS. are added together with thepick up Ke from the non-directional antenna A.'N.D. If Ke is greaterthan never to Zero) by ce cos 0f(t) -l-pe sin 0f(t) The instantaneouszero-amplitude of modulation of the detected and ltered signal, which isindicated at the input of tube VD in Fig. 3 by sharp peaks, occurs whence` cos HIGH-lie sin 0f' (t) :0, i. e. when tan 6 j@ :c The y axis ofthe oscillograph is understood to be represented by a line on thesurface of the oscillographA screen perpendicular to the Y deflectorplates so that the y axis will represent the path traced by theoscillograph spot if an alternating potential is applied to the Y platesonly. The :1: axis is then a similar line related to the X plates. Sincethe waves f, f', applied to the plates are different in wave form, forexample in frequency, the pattern traced if the spot were effective atall times would vary so as to cover the face of the screen with a givenpattern. Since the peaks occur at the time when the ratio w fu) and onlyat this time is a spot indicated on the oscillograph screen, it is clearthat the screen will only be illuminated at points where the parwhichwill satisfy the conditions as outlined with the structure of Fig. 3, isone in which 6=45. At the same time the peaks will occur to control thespot of light, a line will be indicated on the oscillograph at 45 to thex and y axes of the screen which corresponds to the direction of thesource.

Thus, if the oscillograph operates only when the instantaneousmodulation amplitude equals Zero, then the diagram will be a straightline pointing in the direction of the transmitter.

By the use of different modulating wave-forms the whole of theoscillograph screen is scanned and the direction is indicated by a linewhich extends to the edge of (or even beyond) the circular compassscale.

The particular method of selection of Zero amplitude of modulation shownin Fig. 3 picks out alternate zeros, and the line drawn on theoscillograph extends in one sense only from the centre of the screen,thus giving no ambiguity of sense of the signal.

If the non-directional signal Kc is omitted the envelope of the highfrequency wave passed through the ampliiier A gives twice as many maximaand twice as many minima as for the case when a non-directional antennais used and Ke is added. The production of peaks by the same method asbefore does not indicate zero amplitude from the modulators, but a meanamplitude. These peaks, however, may still be used to indicate directionon the oscillograph.Y In this case, the number of peaks being doubled,direction but not sense of the signal will be indicated.

As shown in Fig. 4 the coils of the low frequency oscillator modulatorvalves V.N.S. and V.E.W. may be connected as the ield coils FCS- FCi ofa dynamo-meter indicating instrument. When the oscillator portions ofV.N.S., VFW. operate at frequencies f1 and f2, then modulation of thesignal is produced at each of these frequencies. 'This produces a fieldwhich varies with time since the potentials vary with time under controlof f1 and f2. If, now, the output from detector D is taken to a searchcoil S suspended in the iield of the coils FCl-FCIL' each oscillatorexerts a couple on the search coil S according to the strength of themodulation at fr (for one oscillator) and f2 (for the other oscillator).The total effective held upon the search coil, varies then not only withthe impressed eld on the eld coils but also in proportion to the currentin the search coil. Thus, the

direction is indicated by the resultant iield forces i in a manneranalogous to that more fully explained in connection with Fig. 3. Theresult is that the search coil S takes up a position corresponding tothe direction of the incoming signal.

It will be noted that in this arrangement the output from the detector Dis applied directly to the search coil S. The deliberate distortion ofthe wave form employed for the oscillograph indication described withreference to Fig. 3 is not necessary. It will be noted that simplemodulators are employed in Fig. ll. Although the symmetrical circuit asused in Fig. 3 is likely to give the best results in practice there isno theoretical reason why two simple modulators only should not be used.i

The invention is of course not limited to the precise arrangementsdescribed and many modications will readily occur to be versed in theart. The modulation of the signals is conveniently carried out byheptode valves, but any modulating device could be used including bothelectrical and mechanical methods. For electrical methods, metalrectifiers, diodes, triodes, tetrodes, pentodes, etc., are obvioussolutions. The modulating wave forms are most conveniently provided bysimple low frequency oscillators but any wave forms could be used.Moreover, Whilst two methods for the comparison of the modulationenvelope with the modulating wave have been described numerous othermethods could obviously readily be evolved.

The directional aerials A.E.'VV., ANS. may be loop aerials but largerstructures could be used, such as are employed, for example, in Adcockdiiection finding systems. Instead of the conventional north-south andeast-west aerial systems four completely separate non-directionalaerials may be used with individual associated modulators.

The aerials ABW. and ANS. are not necessarily disposed at right-angles.They have been described as being at right-angles only because it ismore convenient to design an indicating device with controlling forcesoperating at right angles.' The loops could be arranged at any angleprovided a corresponding disposition were given, for example, to thefield coils FCL- FCLi in Fig. 4l.

Any type of amplier and detector may be used. The use of a singleamplifier and detector is convenient but two separate amplifiers anddetectors could be used, one for the north-south signal and the otherfor the east-west signal.

An exact balance of the two directive aerial systems is not necessary,nor an exact balance of the two modulators. A compensation for unbalancemay be eiected by controls operating upon the amplitude of signals fromone antenna system, sensitivity of a modulator, a relative sensitivityof north-south and east-west indications on the indicating device, orthe amplitude of input to the indicator of either modulating wave forms.A Calibrating signal may be used vforI effecting a balance of thesystem.

Any site error or error due to unbalance in the indicating device may becompensated for as described in the preceding paragraph, by mechanicalrotation or" either of the aerial systems, or by adjustment of directionof the eld coils in Fig. L or the deector plates of the oscillograph inFig. 3. For example, the northsouth bearing is corrected on theindicating device by rotation of the east-west aerial particularly ifthis is a loop. Similarly the exact eastwest bearing is corrected byrotation of the north-south aerial. Any remaining errors which may beevident at NW, SVT, SE or NE may now be compensated by adjustment of onemodulating wave-form input to the indicating device. When theseadjustments have been made, a small octantal error, only, is possible.

The broad principle of the invention as dened by the appended claims isalso applicable to systems for automatically indicating the polarisationof incoming electromagnetic waves, and for automatically indicating thedirection of sound waves.

What is claimed is:

l. Apparatus for giving a direct indication of the direction of waves,comprising at least two wave collectors, means for producing twomodulating waves of diierent wave form, means for modulating the signalsreceived by one of said collectors with one of said modulating waves andthe signals received bythe other of said collectors with the other ofsaid modulating waves and for combining said modulated signals, andmeans controlled jointly by said combined modulated signals and saidmodulating Waves, and responsive to the relation between said combinedmodulated signals and said modulating waves for indicating the relativestrengths of the signals received by said collectors.

2. A device for giving a direct indication oi the direction of incidentelectromagnetic waves, comprising two directional wave collectors thedirections of maximum pick-up of which are arranged at an angle, meansfor producing two modulating waves of different wave forms, means formodulating the signals received by one of said wave collectors with oneof said modulating waves and the signals received by the other of saidwave collectors with the other of said modulating waves and forcombining said modulated signals, and means controlled jointly by saidcombined modulated signals and said modulating waves, and responsive tothe relation between said. modulated signals and said modulating wavesfor indicating the relative strengths of the signals received by saidwave collectors.

3. Apparatus for giving a direct indication of the direction of incidentelectromagnetic waves, comprising two directional wave collectors thedirections of maximum pick-up of which are arranged at an angle, meansfor producing two modulating waves of different wave form, means formodulatingthe signals received by one of said wave collectors with oneof said modulating waves and the signals received by the other of saidcollectors with the signals of the other of said modulating waves andfor combining said modulated signals, means for deriving a controlsignal from said combined modulated signals, a cathode ray oscillographfor producing Va spot of variable brilliancy and controllable position,means for controlling the brilliancy of said spot by said controlsignal, and means for controlling the position of said spot by saidmodulating waves.

4. Apparatus for giving a direct indication of the direction of incidentelectromagnetic waves, comprising at least two directional wavecollectors the directions of maximum pick-up of which are arranged at anangle, means for producing two modulating waves of diiferent wave form,means for modulating the signals received by one of said wave collectorswith one of said modulating waves and 4the signals received by the otherof said wave collectors with the other of said modulating waves and forcombining said modulated signals, means for deriving a control signalfrom said combined modulated signals, a dynamometer having field coilsand a search coil movable relative thereto, means for energizing saidsearch coil with said control signal, and means for energizing said ieldcoils with said modulating waves.

5. Apparatus as claimed in claim 2, further comprising a non-directionalwave collector and means for combining the signals received by saidnon-directional collector with said modulated signals.

6. Apparatus as claimed in claim 2, wherein said means for modulatingthe signals received by one of said collectors with one of saidmodulating waves and the signals received by the other of said wavecollectors with the other of said modulating waves and for combiningsaid modulated signa-ls, comprises a balanced thermionic modulator foreach of said signals to be modulated, and means for combining theoutputs of said modulators.

7. Apparatus as claimed in claim 2, wherein said means for modulatingthe signals received by one of saidcollectors with one of saidmodulating waves and the signals received by the other of said wavecollectors with the other of said modulating waves and for combiningsaid modulated signals, comprises a thermionic valve: for each of saidsignals to be modulated, connections whereby each of said valvesoperates as a combined oscillator and modulator, and means for combiningthe outputs of said valves.

8. Apparatus as claimed in claim 3, wherein said means for deriving acontrol signal from said combined modulated signals comprises means fordetecting said combined modulated signals, and means for producing fromsaid detected signals a peaky wave form having peaks corresponding toalternate instants of zero amplitude of the envelope of the combinedmodulated signals.

9. Apparatus as claimed in claim 3, wherein said means for deriving acontrol signal from said combined modulated signals, comprise means fordetecting said combined modulated signals, means for modifying saiddetected signais to produce a square wave form, means for convertingsaid square wave form into a peaky wave form, and means for passingalternate ones only of said peaks.

l0. Apparatus for giving a direct indication of the direction ofincident electromagnetic waves, comprising two directional wavecollectors and a non-directional wave collector, means for producing twomodulating waves of different frequency, means for modulating thesignals received by one of said wave collectors with one of saidmodulating waves and the signals received by the other of said wavecollectors with the other of said modulating waves and for combiningsaid modulated signals, means for combining both of said modulated waveswith each other and with the signals received by said nondirectionalcollector, and means responsive to the rela-tion between said combinedsignals and said modulating waves for indicating the relative strengthsof the signals received by said directional wave collectors.

CHARLES WILLIAM EARP.

